Several soy protein products are available commercially for use in foods. However, the greatest obstacle to greater use of soy products in food for human consumption is their undesirable flavor. When soy products are used as food ingredients they release bound flavors upon thermal processing and also generate reactants that may produce flavors. The problem may be compounded if those off flavors are carried through the manufacturing process and trapped in the finished product. The off flavor problem has been difficult to solve because of the low concentration of flavor forming precursors in the soy protein and their complicated interactions. Soy flavor development is believed to be mainly related to an enzymatic oxidation reaction of the polyunsaturated fatty acids with the lipoxygenase and peroxidase contained in soy. Soluble sugars in soybeans are also considered to be associated with flavor formation when subjected to thermal processing.
Although many of the undesirable soy flavors have been identified and can be extracted with organic solvents, such as a hexane-ethanol azeotrope and hot 95% ethanol, these treatments increase production costs and impair protein functionality while providing only marginal flavor improvement. Furthermore, the reversion flavor development of textured soy protein during thermal processing is a serious problem which has not been resolved in the area of human food application. Accordingly, it would be desirable and it is an object of the present invention to provide an improved method for the removal of undesirable flavors from textured soy protein to thereby render it more palatable to human consumers.